PH58371: CICS Liberty JVM server - Threadlocal based memory leak

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Customer observed sustained high CPU due to excessive time spent
  in JVM Garbage Collection (GC).
  
  Dump analysis showed the root cause is a threadlocal based
  memory leak of objects of type
  com.ibm.cics.wlp.jta.impl.CICSUOWEventListener$1
  
  This is similar to PH40286, where the issue was resolved for the
  late-binding case.
  
  This APAR was taken to fix an additional code path that can
  can result in the same leak.
  

Local fix

• 1. If your applications in Liberty do not make use of CICS
  services you can bypass this issue by running the JVM server in
  STANDARD mode rather than INTEGRATED mode.
  
  2. To reduce the operational impact of sustained time in GC,
  especially on z/OS systems with a high number of processors and
  business critical shared workloads, throttle the number of GC
  Worker threads explicitly using the switch:
  -Xgcthreadsn
  where n is the maximum number of GC Worker threads that will be
  created.
  This switch can be coded in the jvmprofile file used for the
  CICS JVM server involved.
  This second point is intended to help ameliorate the effect of
  sustained time in GC.
  It does not address or bypass the memory leak.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS users.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: A Java memory leak occurs when no CICS  *
  *                      Task previously exists and then is      *
  *                      subsequently not created in the period  *
  *                      between a Liberty UserTransaction begin *
  *                      and end.                                *
  ****************************************************************
  CICS registers a UOWEvent Listener when a Liberty JVM server is
  enabled in order to enlist CICS resources in a UserTransaction
  if necessary.
  However if a UserTransaction begins and ends without a CICS
  Task being created, then the UserTransaction's Listener is not
  removed.
  
  Under sufficient load this small leak can cause a Java
  OutOfMemoryError
  

Problem conclusion

• CICS was updated so that the Listener is removed when the
  transaction end occurs (through Commit or Rollback).
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UI96020 UI96021

Modules/Macros

• DFJ@H415
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R200 PSY UI96020

     UP24/03/12 P F403 ¢

• R300 PSY UI96021

     UP24/03/12 P F403 ¢

Fix is available

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